1. Field of the Invention
The present invention relates to a lithographic apparatus and a device manufacturing method.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays, and other devices involving forming fine structures. In a conventional lithographic apparatus, a patterning means, which is alternatively referred to as a mask or a reticule, may be used to generate a circuit pattern corresponding to an individual layer of the IC (or other device), and this pattern can be imaged onto a target portion (e.g., part of one or several dies) on a substrate (e.g., a silicon wafer, glass plate, etc.) That has a layer of radiation-sensitive material (e.g., resist, photoresists, etc.). Instead of a mask, the patterning means may be dynamic and include an array of individually controllable elements, which serve to generate the circuit pattern.
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction), while synchronously scanning the substrate parallel or anti-parallel to this direction.
Because of the high capital costs of masks used in conventional lithographic apparatus, various proposals have been made to replace the mask by a programmable device, such as a liquid crystal display, a micro-mirror array, a grating light valve, or the like. A mask pattern is digitally loaded into the programmable device, which spatially modulates the projection beam so that a desired pattern is projected onto the substrate. This enables smaller production runs of a given pattern to be produced economically and allows one or more changes to the pattern to be made dynamically or in real-time, which reduce the prototyping cycle. Suitable programmable devices, also referred to as spatial light modulators, programmable patterning devices, dynamic pattern generators, or the like, have the drawback that they emit quite narrow beams, i.e., with a low NA, whereas a high NA is desirable to increase the resolution of the projected image.
Therefore, what is needed is a system and method that provide a lithographic apparatus employing a programmable patterning means that also has a high effective NA at a substrate plane.